An armature and a field magnet arrangement for a generator can be assembled in various successive assembly stages. In one example of a rotor assembly procedure, various components such as a bearing and a hub interface are mounted in a first assembly step to a hollow annular rotor shaft. A form-retaining element can be temporarily mounted onto the rotor so that this maintains its circular shape during the assembly stages. A circular shape is mandatory, considering the weight of the magnet poles. The stator can be merged with the rotor at one assembly stage, for example by connecting the stator shaft to the previously mounted bearing. In this step, extreme care must be taken to maintain a constant air gap between the rotor and the stator. In a subsequent assembly step, cabling can be installed and connected. In another step, the magnets can be mounted onto the rotor. In a final stage, a brake disc is mounted onto the rotor. This assembled part of the generator can then be transferred to a next assembly area for incorporating into a nacelle.
A conventional wind turbine generally comprises a gearbox to increase the rotational speed of its generator relative to its rotor shaft and to increase the pole change frequency. A gearbox comprises many components that are subject to wear and must be maintained or replaced at intervals. Complex and expensive bearing arrangements are also required to bear the extreme loads and torque acting on the rotor shaft and the gearbox. A direct-drive wind turbine has several features over such a conventional wind turbine, whereby a major feature is that a direct-drive turbine does not require such a gearbox. A direct-drive wind turbine requires fewer parts, is less complex, and more reliable. For these reasons, demand for direct drive wind turbines is increasing.
A direct-drive generator has a relatively large diameter and many magnets of altering polarity arranged along a circumference of a field magnet arrangement—usually an outside rotor—to allow for a sufficiently high pole-change frequency. The physical dimensions and weight of such a large generator pose problems during its assembly. Handling of the heavy, unwieldy and vulnerable components is complex and time-consuming, and is also hazardous, so that strict safety measures must be adhered to. This adds considerably to the overall time and cost required for the assembly of a direct-drive generator. In prior art assembly methods, a generator can be assembled in one location, i.e. any parts or tools needed for the assembly are brought to that location, and then removed to another location when no longer needed. Alternatively, a partially assembled rotor or generator assemble can be moved from one assembly area to another using equipment that is capable of carrying the heavy loads, for example cranes or other hoisting apparatus. Since several generators might be assembled simultaneously, the known methods involve much transport and moving of partially assembled generator components, tools and parts, and the risk of damage to a sensitive precision component such as a stator or a rotor is very high. For these reasons, the known methods are costly and time-consuming.